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News in climate science and exploring boundaries : A Policy brief on developments since the IPCC AR4 report in 2007

Rapport | 01-12-2009

The IPCC Fourth Assessment Report of 2007 (AR4), today, still offers a solid scientific base for climate policy-making. However, there are risks of climate change happening faster - or having more severe impacts – than expected. Therefore, it is recommended that climate monitoring efforts be increased, and policy response options which address these risks are investigated.

The IPCC Fourth Assessment Report of 2007 (AR4), today, still offers a solid scientific base for climate policy-making. However, there are risks of climate change happening faster - or having more severe impacts – than expected. Therefore, it is recommended that climate monitoring efforts be increased, and policy response options which address these risks are investigated.

Warming continues

Global warming is continuing. Over the last 10 years, global average temperatures have been increasing at a slower rate, but this is due to natural variations that are well understood. In addition, eight of the ten warmest years on record occurred in the period since 2000. The Greenland and Antarctic Ice Sheets are melting at a faster rate than was estimated in 2007, and the surface area and thickness of the sea ice in the North Pole area are ever decreasing. However, in the coming decades, the sun might become less active than it is today; this could slow down global warming in the coming 20 to 30 years with 0.2 °C. In the last few years, the increase in greenhouse gas emissions has tended to slow down. For this year, even a slight decrease is expected, partly due to the economic crisis.

Warning signs

The IPCC report assumes the most likely scenario for climate change. PBL, however, states that some attention needs to be paid to the risks involved in scenarios of faster global warming. Although the chances of such increased global warming are slight, global or local effects could be very large. For instance, it could lead to dieback of the Amazon rainforest and the boreal forests. The report recommends looking for warning signs that provide early indication of an acceleration of climate change, as well as recognising its possible effects. The PBL also suggests that further research be done into the policy measures meant to deal with these types of risks, such as those limiting greenhouse gas emissions, or those aimed at adaptation to climate change.